Liquid reaction molding (also called Reaction injection molding or liquid injection molding hereinafter LRM or LIM) of solid polyurethane articles from a liquid mixture of polyol and isocyanate has become increasingly important as a means of molding large articles without going to the extremely high mold clamping pressures and forces required for ordinary injection molding. For example, for an automobile body part (rear or front fascia) weighing about 10-15 pounds, the liquid or reaction injection system uses mold closing forces and pressures of about 60 tons and about 100 psi. respectively, whereas injection from a plasticated mass of rubber or thermoplastic polymer of about the same weight may involve mold cavity pressures on the order of 8000 psi. and clamping force on the order of 3000 tons or greater.
The technical literature describes liquid or reaction injection molding. The January, 1975 edition of Plastics Engineering, pps. 25-29 describe a number of products being made by this technique as well as some of the systems. A number of U.S. patents describe components of such systems, e.g. U.S. Pat. No. 3,410,531 and 3,409,174.
It is sometimes desired to vent the mold of gases originally therein and to degas the reacting mixture before it solidifies. These are often accomplished by mold design and venting. Sometimes it is required to tip the mold in order to permit the gas bubbles to rise to a vent at the mold high point.
An objective is to present an embodiment of a clamp or press which can swing a mold thereby to vent it or otherwise to improve the LIM process.
The present trend toward molding large parts such as a complete automobile fender, bumper, or auto body front or rear end by liquid injection has generated a daylight requirement. Daylight is a trade term used to describe the space available for a molding to drop out of the mold. The amount of daylight is normally directly proportional to the size of the press or clamp in which the mold parts are mounted. Where large parts such as those mentioned are to be made by liquid injection molding a large daylight requirement results which ordinarily would require a high tonnage large clamp.
Accordingly, an objective of the present invention includes providing an apparatus for liquid injection molding. A LIM apparatus having large daylight is an objective also.
The large daylight requirement for LIM as well as the need to mount and demount large molds (some weigh 10 to 15 tons) are incompatible with the tie rod type of construction typically used in conventional injection molding machines. The present invention features a C-frame in which mold parts are pivotally mounted. This structure eliminates tie rods, increases daylight, enhances access to the mold (no hands in the die), facilitates mold mounting, and maintains mold alignment despite deflection of parts of the C-frame.
The moving of a mold or rather of the closed mold around a path is, broadly speaking, already known. It is known for example to move closed molds or the components thereof through horizontal and vertical circular paths, these being nicknamed merry-go-round and ferris wheel arrangements. U.S. Pat. No. 3,663,139 illustrates a representative merry-go-round.
The invention therefore relates to a clamp for mounting mating parts of a mold in the mold cavity of which may be reacted an organic liquid molding to form a solid molded object comprising a C-shaped frame assembly having a lower jaw connected by a column to an upper jaw; a mold support (crown) pivotally mounted on the upper jaw of said frame assembly; a pedestal and floor plate assembly; means revolvably supporting said C-shaped frame assembly from said pedestal and floor plate assembly; a mold bed support (bed) pivotally mounted on the lower jaw of said frame assembly; the pivotal mounting means for said crown and bed being located on parallel axes; and a movable platen reciprocably mounted on one of said bed and said crown; said crown and said movable platen being adapted to support thereon respective parts of said mold and positionable so that the mold is closed when the crown and platen are substantially parallel and said platen advanced to where the mold parts are engaged and said mold is opened by retracting said platen and pivotally swinging both said base and crown away from the column portion of said frame assembly.